1. Field of the Invention
The present invention relates to the field of beneficiation of mineral substrates by removing undesired impurities. Specifically, the present invention relates to a magnetic reagent and a method of using it in a magnetic separation process to reduce the levels of the impurities in the mineral substrates.
2. Description of the Related Art
Beneficiation is a term used in the mining industry to refer to various processes for purifying mineral substrates (such as mineral ores) to obtain value minerals. Beneficiation typically involves separating the desired or “value” minerals from other less desirable or “non-value” mineral(s) that may be present in the mineral substrate. In many cases, the degree of separation obtained strongly influences the quality of the beneficiated product. For example, value minerals such as kaolin, talc, and calcium carbonate are used as pigments in a variety of end applications, e.g., coatings and fillers in paper, paint, plastic, ceramics, etc. In such applications, desirably higher levels of whiteness or brightness are typically associated with lower levels of impurities. However, value minerals often contain a variety of discoloring minerals such as titanium and iron phases. For example, kaolin typically contains anatase (TiO2) and iron oxides, which detrimentally affect the brightness of kaolin. Also, minerals with relatively low impurity levels are often desired in other applications, such as in the electronics, optics and biomedical fields.
Some mineral separation processes involve the use of magnetic reagents and strong magnetic fields. PCT Publication WO 02/066168 discloses surface-functionalized magnetic particles that are said to be useful as magnetic reagents for mineral beneficiation. The magnetic particles are said to be at least comparable in size with the mineral particles, and thus it is apparent that the amount of material present on the surfaces of the magnetic particles is only a small part of the magnetic reagent. U.S. Pat. Nos. 4,834,898 and 4,906,382 disclose magnetizing reagents that are said to comprise water that contains particles of a magnetic material, each of which has a two layer surfactant coating including an inner layer and an outer layer. The inner and outer surfactant layers on the magnetic particles are said to be monomolecular, and thus it is apparent that the amounts of surfactants in the magnetic reagent are very small as compared to the amounts of magnetic particles.